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A325392 Number of permutations of the multiset of prime factors of n whose first part is not 2. 2
1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 2, 0, 1, 2, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 4, 1, 0, 2, 1, 2, 3, 1, 1, 2, 1, 1, 4, 1, 1, 3, 1, 1, 1, 1, 2, 2, 1, 1, 3, 2, 1, 2, 1, 1, 6, 1, 1, 3, 0, 2, 4, 1, 1, 2, 4, 1, 4, 1, 1, 3, 1, 2, 4, 1, 1, 1, 1, 1, 6, 2, 1, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,15

LINKS

Table of n, a(n) for n=1..87.

FORMULA

If n is odd, a(n) = A008480(n). If n is even, a(n) = A008480(n) - A008480(n/2).

EXAMPLE

The a(90) = 9 permutations of {2,3,3,5} not starting with 2:

  3 2 3 5

  3 2 5 3

  3 3 2 5

  3 3 5 2

  3 5 2 3

  3 5 3 2

  5 2 3 3

  5 3 2 3

  5 3 3 2

MATHEMATICA

primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];

Table[Length[Select[Permutations[primeMS[n]], #=={}||First[#]>1&]], {n, 100}]

CROSSREFS

Number of times n appears in A325390.

Cf. A008480, A056239, A112798, A325327, A325362, A325364, A325367, A325403, A325407, A325460, A325461.

Sequence in context: A249147 A260648 A127242 * A025853 A228247 A025847

Adjacent sequences:  A325389 A325390 A325391 * A325393 A325394 A325395

KEYWORD

nonn

AUTHOR

Gus Wiseman, May 02 2019

STATUS

approved

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Last modified January 28 00:32 EST 2020. Contains 331313 sequences. (Running on oeis4.)